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  1. #1
    hpulley's Avatar
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    Focusing t-grain vs. traditional grain negatives

    Where do you focus with t-grain films? Not sure if this is a question for this subforum or the B&W film and paper group but here goes:

    I used to print ages ago but back then I never used t-grain films, just traditional ones. Now I've been shooting some of both, HP5+ and FP4+ which I always used and enjoyed and some Delta of various speeds as well. Since the time when I used to do darkroom before I mostly had others do the dev and printing so I didn't look for this but now that I'm doing both myself again I guess I'm finally paying attention and I noticed that e.g. HP5+ has a flat 2-D grain structure while the Delta 400 and 3200 films have a deeper 3-D structure. Delta 100 is fairly tight and the grain is very small anyways so this is more a question about the fast films.

    Back to my question, with HP5+ it is obvious where to focus using the grain 'scope, as you move the focus the whole 2-D structure comes into focus essentially at once. With the fast Delta films instead there is a 3-D lattice which comes into focus. Do I aim for the middle of this, the top, the bottom? Does it really matter if I'm going to stop the El-Nikkor down to f/8 anyways?
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

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  2. #2

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    Focusing at Selective Depths in a Film Emulsion

    This doesnít make sense in my experience. Modern film emulsions are extremely thin. This article puts it at less than .001Ē (.0254mm) thick.

    http://electronics.howstuffworks.com/film3.htm

    Itís inconceivable that you, I, or anyone could perceive focus at various depths of the emulsion with a typical 2-element 20X grain focuser. If the grain structure at any depth is in focus, then so too is all of it.

    Even if this were the case, how could the focusing mechanism of an enlarger be moved in small enough increments to alter focus selectively from one depth of the emulsion to another? Can you alter the lens to negative distance in .0005Ē (0.0127mm) increments or finer? I donít think itís possible with the focusing mechanisms enlargers are equipped with.

    To discern the grains at various depths in the emulsion would require a very powerful microscopeómore likely an electron microscope.

    Itís usually much easier to focus by closing the lens to the working aperture to grain focus. This makes the grain much more well-defined and seems to have better contrast than trying to focus with the lensís aperture wide open. Itís also much more comfortable to the eye, since the bright light will be reduced to 1/4th itís original intensity by stopping down 2 stops.

    Iíve used many types of films since 1985. I havenít noticed any difference in how I perceive the grain as I refine the focus, only differences in grain size and pattern.

  3. #3
    hpulley's Avatar
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    Thanks for your reply.

    I'm just reporting what I see which is that there are layers of grain in the Delta 400 and 3200 films, it is obviously deeper in structure than HP5+. Perhaps I'm not knowing what I'm looking about but with the old coarse knob on the Durst M-300 with 50mm f/2.8 El Nikkor this is what I see... I find it easier to find precise focus at f/2.8, at smaller aperture the depth of field makes it looks in focus over a wider range.
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

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  4. #4
    ic-racer's Avatar
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    Focus on the "far" grain structure, then move the enlarger head up to get the "near" grain structure in focus. The change in distance on the enlarger column between the two head heights can be used to calculate the actual depth of what you are seeing by using the simple lens equation:

    1/f = 1/p1 + 1/q1
    1/f = 1/p2 + 1/q2
    with emulsion depth = p1-p2

    Where:
    f = focal length of enlarging lens
    p1 = near distance from lens to baseboard
    p2 = far distance from lens to baseboard
    q1 = distance from lens to top of emulsion
    q2 = distance from lens to bottom of emulsion
    q1-q2 = depth of emulsion

  5. #5
    hpulley's Avatar
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    Thanks for the equations. I'm not sure that there is enough movement in between for me to get a measurable distance with the tools I have but I'll see what I can do.
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

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  6. #6
    Jerevan's Avatar
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    Ic-racer,

    do you see the same thing as hpulley does? You must be doing serious enlargments or use pretty some high-res grain focus. I've never seen anything except that it is really hard to find the grain on T-grain films.
    ďDo your work, then step back. The only path to serenity.Ē - Lao Tzu

  7. #7
    hpulley's Avatar
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    Quote Originally Posted by Jerevan View Post
    Ic-racer,

    do you see the same thing as hpulley does? You must be doing serious enlargments or use pretty some high-res grain focus. I've never seen anything except that it is really hard to find the grain on T-grain films.
    You're shooting 35mm Delta 400 and 3200? Enlarging to 11x14"? Am I crazy? Perhaps I don't want an answer to that one but I see what I see, not sure these eyes are shot. Perhaps I can project the image, hook my macro lens and Bellows FL up to a camera and take a picture of the grain at near, middle and far focus so you people believe me.
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

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  8. #8
    Jerevan's Avatar
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    Okay, I have only done Tmax 100 (and Ilford 3200 but that was so long ago that I can't be held responsible for it!) so I am just interested in what you are able to see. And no, you're not totally crazy - I've done close to 11x14" with HP5+.
    ďDo your work, then step back. The only path to serenity.Ē - Lao Tzu

  9. #9
    Nicholas Lindan's Avatar
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    What you are seeing are diffraction patterns on either side of the actual focus point. They are an artifact of the interaction of the film, the enlarging lens, the grain magnifier, eyeglasses or contacts and your eyes.

    If you are focusing with eyeglasses on try taking them off - you may have to refocus the magnifier.

    If you are stopping down to f8 I wouldn't worry too much - the only meaningful test is to ask "Are the prints sharp?"

    I find I can focus just as accurately without a grain magnifier as with - a benefit of horrid nearsightedness.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  10. #10

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    Why not make two prints and compare the results? Print one, focus on the near edge. Print two, focus on the far edge. Process both and compare the results.

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